The present invention relates to apparatus for softening water; and particularly to systems for controlling regeneration of the resin in a water softening apparatus.
It is quite common for water drawn from a well to be considered “hard” in that it contains di-positive and sometimes tri-positive ions which have leached from mineral deposits in the earth. Such ions form insoluble salts with common detergents and soaps producing precipitates that increase the quantity of detergent or soap required for cleaning purposes. When hard water is used in boilers, evaporation results in the precipitation of insoluble residues that tend to accumulate as scale.
It is common practice to install a water softener in the plumbing system of a building that is supplied with hard water. The most common kind of water softener is an ion exchange apparatus that has a tank which holds a bed of resin through which the hard water flows to remove undesirable minerals and other impurities. Binding sites in the resin bed initially contain positive ions, commonly unipositive sodium or potassium ions. As hard water enters the resin, competition for the binding sites occurs. The di-positive and tri-positive ions in the hard water are favored due to their higher charge densities and displace the unipositive ions. Two or three unipositive ions are displaced for each di-positive or tri-positive ion, respectively.
The capacity of the resin bed to absorb minerals and impurities is finite and eventually ceases to soften the water when a large percentage of the sites become occupied by the di-positive and tri-positive ions. When this occurs, it becomes necessary to recharge or regenerate the resin bed by flushing it with a regenerant, typically a solution of sodium chloride or potassium chloride. The concentration of unipositive ions in the regenerant is sufficiently high to offset the unfavorable electrostatic competition and the binding sites are recovered by unipositive ions. The interval of time between regeneration periods during which water softening takes place is referred to as a “service cycle.”
Regeneration of early types of water softeners was affected manually only after it was discovered that the treatment capacity of the resin bed has been exceeded and the water flowing there through is no longer “soft.” In an effort to eliminate the need for manual regeneration, water softener control systems were provided with a mechanical clock which initiated water softener regeneration on a periodic basis. The frequency of such regeneration was set in accordance to the known capacity of the resin bed and the anticipated daily usage of soft water. Although mechanical clock-type water softener controllers alleviated the need for manually regenerating the resin bed, such controllers are subject to the disadvantage that regeneration at fixed intervals may occur too often or not often enough depending upon water usage. Regenerating the water softener resin bed when sufficient capacity to treat water still exists wastes the regenerant and the water used in regeneration. Conversely, failure to regenerate the water softener after the resin bed capacity has diminished to a point below that required to treat hard water may result in hard water leaving the water softener.
In an effort to better regulate the frequency of water softener regeneration, demand-type water softener controls have been developed which determine the remaining capacity of the resin bed to soften water. One type of such an improved control system is disclosed in U.S. Pat. No. 4,426,294 in which a flow meter measures the volume of water being treated and regenerates the resin bed when a specified volume of water has flowed through the softener since the previous regeneration. While this type of system is adequate in many installations, municipal systems alternately may draw water from several wells which contain water having different degrees of hardness. In that case, the exhaustion of the resin bed is not a direct function of the volume of water which has been treated since the previous regeneration.
Other types of control systems were developed which detect the exhaustion of the resin bed directly. For example, U.S. Pat. No. 5,234,601 utilizes electrodes to measure the electrical conductivity of the resin bed at two spaced apart locations. The ratio of the conductivity measurements, along with the minimum and maximum ratio values that occurred since the previous resin bed regeneration, are used to determine a probability of resin bed exhaustion and this trigger regeneration.
In this conductivity based system, wires extend from the controller through the opening at the top of the resin tank through which the water also entered and exited the tank. Thus the wires and their connection to the sensing electrodes were exposed to the water and to the brine solution used during regeneration. That exposure often had a deleterious effect on the wires and the electrode connection.
The present inventors proposed solving this problem by extending the electrodes through the sidewall of the resin tank, however this approach was complicated by the curved sidewall of the tank. In addition, some resin tanks have a polyethylene liner within a fiberglass outer shell and the liner is not adhered to the shell which makes a water tight connection between the electrode and the tank very difficult.
Therefore, it is desirable to provide a water tight assembly for inserting the conductivity sensing electrodes through the sidewall of the resin tank in a water tight manner.